The present invention relates to a mask for use in photolithography and its manufacturing technique, and particularly to a technique effectively applicable to a mask for use of manufacturing semiconductor integrated circuit device.
In recent years, very fine elements constituting a circuit, very fine wirings and very narrow spaces between the elements and wirings have been developed in semiconductor integrated circuit devices.
However, along with such development of the elements and wirings and of the spaces between elements and wirings, there arises a problem in that the accuracy of mask pattern transfer is lowered when an integrated circuit pattern is transferred onto a wafer by coherent light.
This problem will subsequently be described with reference to FIGS. 24(a)-(d).
When a given integrated circuit pattern formed on a mask 50 shown in FIG. 24(a) is transferred onto a wafer by a method of projection exposure or the like, the phases of lights each transmitted through each of a pair of transmission regions P1, P2 having light shield region N therebetween are identical to each other as shown in FIG. 24(b). Consequently, these interferential lights increase their intensities in light shield region N located between the above-mentioned pair of transmission regions P1, P2 as shown in FIG. 24(c). As a result, as shown in FIG. 24(d) the contrast of a projected image on a wafer is not only lowered, but also the depth of focus becomes shallow, causing the transfer accuracy of the mask pattern to be considerably lowered.
As a means to counteract these problems, a technique of phase shifting lithography has been developed, whereby the phase of light transmitted through the mask is controlled so as to improve the resolution and contrast of the projected image. The phase shifting lithography technique is disclosed, for example, in Japanese Laid-Open Patent No. 173744/1983 and Japanese Laid-Open Patent No. 67514/1987.
In the above-mentioned Japanese Laid-Open Patent No. 173744/1983 there is described the structure of a mask having a light shield region and a pair of transmission regions, wherein a transparent material is arranged at least in either one of the transmission regions sandwiching the light shield region therebetween, allowing a phase difference to be generated between the lights each transmitted through each of transmission regions at the time of exposure and thus these lights being interfered with each other to weaken themselves in the region on a wafer which should primarily be a light shield region.
The function of the light transmitted through such a mask as above will subsequently be described with reference to FIGS. 25(a)-(d).
When a given integrated circuit pattern formed on a mask 51 shown in FIG. 25(a) is transferred onto a wafer by the method of projection exposure or the like, a phase difference of 180xc2x0 is generated between the phase of light transmitted through a transmission region P2 having transparent material 52 of a pair of transmission regions P1, P2 which have light shield region N sandwiched therebetween and the phase of light transmitted through the normal transmission region P1 as shown in FIGS. 25(b) and (c). Therefore, the lights transmitted through the pair of transmission regions P1, P2 interfere with each other to offset them in light shield region N located between these transmission regions P1, P2. Consequently, as shown in FIG. 25(d), the contrast of a projected image on a wafer is improved. Thus, the resolution and depth of focus is improved, resulting in a higher accuracy of pattern transfer of the mask 51.
Also, in the above-mentioned Japanese Laid-Open Patent No. 67514/1987, there is described the structure of a mask having a light shield region formed by light shielding film and a transmission region formed by removing the light shielding film, wherein a fine aperture pattern is formed by removing a part of shielding film and at the same time, a phase shifting layer is provided on either one of the transmission region or the aperture pattern, and thus a phase difference is generated between the lights transmitted through the transmission region and the aperture pattern, preventing the distribution of amplitude of light transmitted through the transmission region from being spread in the horizontal direction.
Nevertheless, the present inventor has found that the conventional technique disclosed in the above-mentioned Japanese Laid-Open Patent No. 173744/1983 has the following problem:
The above-mentioned conventional technique in which a phase difference is generated between the lights transmitted through the pair of transmission regions does not has any problem as far as a pattern is simply and unidimensionally arranged in a repetitive manner. However, in the case that the pattern is complicated as in an actual integrated circuit pattern, the arrangement of the transparent material may be impossible, and a problem arises in that sufficient resolution is not obtained at some sections.
For example, in the case of an integrated circuit pattern 53 shown in FIG. 26. If transparent material is arranged in a transmission region P2, the resolutions in light shield regions N1 and N2 are certainly improved. However, if transparent material is arranged in transmission region P1 in order to improve the resolution in light shield region N3, the lights transmitted through transmission regions P1, P2 will have an identical phase, causing the resolution in light shield region N2 to be lowered. Also, in order to improve the resolution in the light shield region N3, a transparent material should be provided in such a transmission region as the transmission region P3. Then, the transparent material can be arranged in a part of transmission region P3. In such a case, however, there appears the reversing of phases in the lights transmitted through the same transmission region P3, and an unwanted pattern is formed on a wafer. Consequently, it becomes impossible to improve the resolution in light shield region N3.
Furthermore, if the pattern is complicated like an actual integrated circuit one, the arrangement of transparent material is restricted as mentioned above. This makes it difficult to prepare the pattern data of the transparent material. Conventionally, therefore, the pattern of the transparent material should be produced specially while taking into consideration the above-mentioned restriction on the arrangement when a mask having means for shifting phase of light is manufactured.
On the other hand, the known technique disclosed in Japanese Laid-Open Patent No. 67514/1987, whereby an aperture pattern is formed in a light shield region so as to generate a phase contrast between the light transmitted through the aperture pattern and the one transmitted through the transmission region, makes it difficult to arrange the aperture pattern, the same as in the case of the above-mentioned publication, if a pattern is as complicated and extremely fine as an actual integrated circuit pattern. For example, should the width of pattern of light shield region become narrower, there arises a problem in that the arrangement of an aperture pattern is difficult.
Furthermore, in this conventional technique, no consideration is given as to the lowering of light intensity at the corners of transmission region which takes place along with a further miniaturization of transmission region required, resulting in a problem posed in that the corners of a projected image are rounded.
The present invention is to solve the above-mentioned problems, and the object thereof is to provide a technique whereby the transfer accuracy of a pattern formed on a mask can be improved.
Another object of the present invention is to provide a technique whereby the manufacturing time of a mask having means for shifting phase of light can be reduced.
Still another object of the present invention is to provide a technique whereby the resolution of not only each side of a projected image but also of each corner thereof can be improved.
Among the inventions to be disclosed in the present application, those typical ones will subsequently be described.
Now, the first invention is a mask having light shield and transmission regions and transferring a given pattern at least by irradiation of coherent light locally, wherein a phase shifting portion is formed in a part of the aforementioned transmission region for shifting a phase of light transmitted, and a phase contrast is generated between the light transmitted through the aforementioned phase shifting portion and the light transmitted through the transmission region where the aforementioned phase shifting portion is not formed, and the aforementioned phase shifting portion is so arranged that the interferential lights of the aforementioned lights can weaken themselves in the boundary area of the aforementioned transmission and light shield regions.
The second invention is the method of manufacturing a mask wherein the pattern data of the phase shifting portion can automatically be prepared in accordance with the pattern data of the light shield region.
The third invention is a mask in which light shield and transmission regions are provided on a mask substrate and a given pattern in the mask is transferred at least by the irradiation of coherent light locally, wherein a groove having a depth to reach the main surface of the aforementioned mask substrate is formed, and simultaneously a phase contrast is generated between the light transmitted through the aforementioned groove and the light transmitted through the aforementioned transmission region, and a phase shifting groove is formed on the aforementioned mask substrate located below the aforementioned groove so as to allow the interferential lights of the aforementioned lights to weaken themselves at the end portion of the aforementioned light shield region.
The fourth invention is a mask in which light shield and transmission regions are provided on a mask substrate, and a given pattern is transferred at least by the irradiation of coherent light locally, wherein a groove having a depth to reach the main surface of the aforementioned mask substrate is formed in a part of the aforementioned light shield region, and a phase contrast is generated between the light transmitted through the aforementioned groove and the light transmitted through the aforementioned transmission region, and a transparent film is provided above the aforementioned groove so as to allow the interferential lights of the aforementioned lights to weaken themselves at the end portion of the aforementioned light shield region, and simultaneously, subtransmission regions are formed at the corners of the aforementioned transmission region.
According to the first invention mentioned above, the light transmitted through the phase shifting portion and the light transmitted through the portion where it is not formed interfere with each other to weaken themselves at the boundary portion of transmission and light shield regions so that the bleeding of contour of an image projected on a wafer can be reduced, and the contrast of the projected image can be improved considerably, resulting in a remarkable improvement of the resolution and death of focus.
Particularly, in the present invention, no restriction on the arrangement of phase shifting portion takes place no matter how complicated the pattern is on the mask. Also, there is no difficulty in arranging the phase shifting portion no matter how narrow the width of pattern becomes in the light shield region.
According to the second invention mentioned above, the manufacturing time of a mask having means for shifting phase of the light can be reduced considerably because there is no need for preparing specially any pattern data of transparent film or phase shifting groove.
According to the third invention mentioned above, the light transmitted through the groove and phase shifting groove interfere with each other to weaken themselves, making it possible to reduce the bleeding of contour of a projected image and to improve the contrast thereof so that the solution and depth of focus can be improved remarkably.
According to the fourth invention mentioned above, the light intensity at the corner of a transmission region increases by the arrangement of a sub-transmission region thereat so that not only the resolution at each side of a projected image, but also the resolution at the corner thereof, can be improved.